Extractants and process for concentrating organic acids



Nov. 4, 1947. c. E. STAFF 2,430,086

EXTRACIANTS AND PROCESS FOR CONCENTRATING ORGANIC ACIDS Filed July 2,1942 em/05mm ----l7 ll Y +4 CONCENTRATED AOUfOUS 16 ACID ACID ---/5 1 2gLIQUOR r FRESH EXTRACTANT IZ"' c01v0-sn i l "22 EXTRACTOR 25 arc/aura?20 SPENT 5v, nousous 3 LIQUOR WATER.-

LAYER |v STILL V I 2? WATER RES/DUE] INVENTOR CHARLE 5 ESTAFF BY M@@ 4ATTORNE relatively large volume of extract.

Patented Nov. 4, 1947.

UNITED STATES PATENT OFFICE EXTRACTANTS AND PROCESS FOR; CON- CEN TRATING ORGANIC ACIDS Charles E.Staii', Charleston, W. Va assignor to Carbideand Carbon Chemicals Corporation, acorporation of New York ApplicationJuly 2, 1942 Serial No. 449,392

course, to extract economically and selectively all of the acid from thewater and to produce an extract from which the acid and the solvent caneconomically be recovered. Some extraction processes have met with adegree of success, but so far as I am aware, they are all limited by thelow selective extractive power of the solvent for the acid and by thenecessity of processing a In some processes the extractant employed hasa lower boiling point than the acetic acid and is recovered from theextract as a distillate which may also contain water. In other processesin which the extractant employed has a higher boiling point than theacetic acid, greater efliciency is possible because such processes donot require the distillation of the extractant. So far as I am aware,however, this latter type of process has suffered from the very lowextractive power of the high boiling extractants thus far proposed andalso from contamination of the acid by products of reactions involvingthe extractant which occur during the extraction and recoveryoperations.

I have now discovered that a solvent material which has a higher boilingpoint than the lower aliphatic acids and which comprises an aliphaticnon-cyclic polyether substantially water-immiscible at elevatedtemperatures having in the molecule a oarbon-to-oxygen atom ratio notgreater than 6 to 1 or an aliphatic carboxylic acid having at least 5carbon atoms in the molecule, is a very advantageous extractant for theconcentration of aqueous solutions of acetic acid and .other loweraliphatic acids. Mixtures of these solvent materials may also be used.-The allphatic polyethers are completely etherifled alkyl I ethers ofpolyhydric aliphatic alcohols. Straight chain or branched chainpolyethers may be used,

' but cyclic polyethers are not contemplated hytlris 2Claims.((2160-1541) invention. Of the higher carboxylic acids, those 7 havingnot more than twelve carbon atoms in the molecule are preferred. Thesesolvent materials make possible a greatly increased efllciency in acidconcentration processes since they have relatively high selectiveextractive power for acetic and other lower aliphatic acids andthey areespecially valuable in concentrating aqueous acids of low initialconcentrations.

At the same time the extractants of this invention are relatively stableand resistant to chemical reaction during use in the process. Becausethey contain no reactive alcoholic hydroxyl groups or hydrolyzable estergroups. there is no tendency toward the formation of reaction productsunder The higher aliphatic acid extractants have the additionaladvantage of being resistant to the chemical action of any mineral acidswhich may be present.

Extractants which I have found especially useful in carrying out theprocess or my invention are the dialkyl ethers of the glycols; includingthe diethers of the polyglycols, having the formula R(OCnHsn)zOR' inwhich n is an integer from 2 to 4, inclusive, and a: is an integer from1 to 4, inclusive, represented by the diethers of the mono, di, tri andtetraglycols of ethylene glycol, propylene glycol, and butylene glycol.The etherifying radicals R and-R are such lower alkyl groups as methyl,ethyl, propyl, butyl and pentyl containing not more than five carbonatoms to theradical, including isomeric forms of these groups. The twoetherifying radicals need not necessarily be the same but the ethermolecule should contain at least six carbon atoms. Other extractantmaterials which may be usedinclude the completely etherifled derivativesof other polyhydric alcohols in which the etherifying groupshaye notmore than five carbon atoms to the radical such as, for instance, thepolyalkyl ethers of glycerol, diglycerol and the like. However, thedialkyl ethers of the glycols as set forth above are preferred. r

The lower aliphatic acid may be recovered from the extract bydistillation in efiicient rectifying apparatus; the acid being obtainedin the distillate, and the extractant as aistlll residue which may bereturned directiytothe extraction operations. By so choosing theextractant that there is a large difference between its boiling pointemcient rectification in the distillation step to attain good separation01 the acid distillate. Ii extractable impurities are present in theaqueous acid, it -may be necessary or desirable to puriiy theextractant' obtained as a still residue, for example, by distillation,before it is recycled in the process. Any small amount of the extractantwhich may be dissolved in the aqueous phase may be recovered bydistillation or by any other convenient means. It is preferred tooperate the extraction process under such conditions of temperature andpressure that the particular extractant used will exhibit its maximumselective extractive power and minimum solubility in the aqueous phase.

Auxiliary agents may be used with the extractants if desired, for thepurpose of purifying or otherwise treating the aqueous lower aliphatictractant to remove acid from the aquous liquor.

The acid-enriched extractant leaves the extractor through line l4 andenters a still IS in which acidthat of the acid distillate, it ispossible to use less rich vapor is distilled from the liquid extract.

The acid-rich vapor leaves the still 15 through a line l6 and acondenser IT. The condensed concentrated acid is withdrawn through lineit.

The liquid extractant leaves thestill l5 through the line .iBand theline l3, and re-enters the extractor I2. The spent (extracted) aqueousliquor leaves the extractor through line 20 and passes f to a still 2!from which is recovered any dissolved extractant as its constant boilingmixture with water. This constant boiling mixture leaves the still 2|through a lin 22 and a condenser '23, and the condensate of extractantand water enters a decanter 25 through line 24. The extractant and waterlayers from the decanter 25 are returned to the extractor l2 and still2i, respectively,

through lines and 28. The aqueous residue withdrawn'from the still 2| byline 21 is substantially free of both the extractant'and the loweraliphatic acid being concentrated in the process. Fresh extractant isintroduced to the extractor I2 asneeded through lines 29 and IS.

The extractive powers of several of the preferred solvent materials aregiven in the following tables. The extractive power is expressed as thedistribution ratio; that is, the quotient of the concentration oftheacid in the extractant layer divided by the concentration of the acid inthe aqueous layer at equilibrium. The concentration of the acid in eachlayer was determined by mixing the extractant substance with anapproximately equal volume of a 10% solution of the acid in water,heating this mixture to 85 C., agitating the mixture and allowing it toseparate into layers while maintained at this temperature. The layerswere then separated, and titrated with sodium hydroxide solution.

In these tables the Roman numerals refer to the following solvents,respectively:

I. Ethylene-glycol diethyl ether II. Diethylene glycol diethyl etherIII. Diezliliyleue glycol methyl (normal) butyl e er IVLEthyleneglycolmethyl (normal) butyl ether V. 2-ethyl butyric acid .Table' A[Distribution ratios at 0.]

\ Add in Solvent menus J I r II III IV V so ution Succinic--.

Table B Distribution ratios at 30 0.]

Solvent aqueous solution Comparable values for the distribution ratiosof acetic acid at 30 C. between octyl alcohol (ethyl hexanol) and waterand between dibutyl phthalate and water are about 0.55 and 0.10, re-

spectively. These values were determined using aqueous solutions ofacetic acid having an initial Table C [Solubility of the solvents inwater as parts solvent per parts water (by weight)] Solvent TemperatureI III IV V The process of this invention may be carried out in astandard apparatus for carrying out' extractions, with appropriateauxiliary stills and separatory vessels, and at elevated temperature.

Depending upon the design of the extractor and the rates of feeding theextractant and the dilute acid liquor, the aqueous phase may besubstantially freed of acid. By way of illustration, diethylene glycolmethyl normal butyl ether is introduced through a dispersing nozzle atthe bottom of a long, upright, packed extraction column; and the diluteaqueous acetic acid (approximately 5%, acetic acid) is introduced at thetop of the extractor through a dispersing nozzle. The aqueous phasedescends'and the extractant phase ascends to effect intimate mixing ofthe two liquids. From the top of the extractor the extract, containingthe extractant, acetic acid and some water, is conducted to a still,from which the relatively concentrated acid is distilled. The extractantremains as a still residue and is removed from the bottom of the stilland recycled to the extractor. The aqueous phase containing somedissolved extractant is removed from the bottom of the extractor andconducted to a still, by means of which the extractant is recovered asan azeotropic' mixture. The condensate from this still is separated intoan extractant layer and a water layer by means of a decanter, and theextractant layer is recycled to the extractor while the water layer isreturned to the still. Fresh extractant is added, as needed, to therecycled and recovered extractant.

As will be apparent from the foregoing, the present invention may bepracticedwith any of the above types of extractant solvents and withprocedures other than those specifically described and under a varietyof conditions of temperatures, pressures, or concentrations ofmaterials. Such modifications are part of this invention and areintended to be included therein.

I claim: 1. Process of concentrating an aqueouswatersoluble loweraliphatic acid which comprises extracting the acid with a liquidextractant and recovering the -lower aliphatic acid from the extract;said extractant having a higher boiling point than said lower aliphaticacid and comprising as an'essential ingredient thereof an allphaticcarboxylic acid having from 5 to 12 carbon I REFERENCES CITED Thefollowing references are of record in the flle ofthis patent:

UNITED STATES PA'IENTS OTHER REFERENCES Hommelen, Chem. Absta, vol. 27,p. 5306 ingredient thereof an ethyl 1

